Statistical models for shear strength of RC beam‐column joints using machine‐learning techniques

This paper proposes a new set of probabilistic joint shear strength models using the conventional multiple linear regression method, and advanced machine‐learning methods of multivariate adaptive regression splines (MARS) and symbolic regression (SR). In order to achieve high‐fidelity regression models with reduced model errors and bias, this study constructs extensive experimental databases for reinforced and unreinforced concrete joints by collecting existing beam‐column joint subassemblage tests from multiple sources. Various influential parameters that affect joint shear strength such as material properties, design parameters, and joint configuration are investigated through tests of statistical significance. After performing a set of regression analyses, the comparison of simulation results indicates that MARS approach is the best estimation method. Moreover, the accuracy of analytical predictions of the derived MARS model is compared with that of existing joint shear strength relationships. The comparison results show that the proposed model is more accurate compared to existing relationships. This joint shear strength prediction model can be readily implemented into joint response models for evaluation of earthquake performance and inelastic responses of building frames. Copyright © 2014 John Wiley & Sons, Ltd.     

Empirical prediction of coseismic landslide dam formation

In this study we develop an empirical method to estimate the volume threshold for predicting coseismic landslide dam formation using landscape parameters obtained from digital elevation models (DEMs). We hypothesize that the potential runout and volume of landslides, together with river features, determine the likelihood of the formation of a landslide dam. To develop this method, a database was created by randomly selecting 140 damming and 200 non‐damming landslides from 501 landslide dams and > 60 000 landslides induced by the M_w 7.9 2008 Wenchuan earthquake in China. We used this database to parameterize empirical runout models by stepwise multivariate regression. We find that factors controlling landslide runout are landslide initiation volume, landslide type, internal relief (H) and the H/L ratio (between H and landslide horizontal distance to river, L). In order to obtain a first volume threshold for a landslide to reach a river, the runout regression equations were converted into inverse volume equations by taking the runout to be the distance to river. A second volume threshold above which a landslide is predicted to block a river was determined by the correlation between river width and landslide volume of the known damming landslides. The larger of these two thresholds was taken as the final damming threshold. This method was applied to several landslide types over a fine geographic grid of assumed initiation points in a selected catchment. The overall prediction accuracy was 97.4% and 86.0% for non‐damming and damming landslides, respectively. The model was further tested by predicting the damming landslides over the whole region, with promising results. We conclude that our method is robust and reliable for the Wenchuan event. In combination with pre‐event landslide susceptibility and frequency–size assessments, it can be used to predict likely damming locations of future coseismic landslides, thereby helping to plan emergency response. Copyright © 2014 John Wiley & Sons, Ltd.     

Granitic coastal geomorphology: applying integrated terrestrial and bathymetric LiDAR with multibeam sonar to examine coastal landscape evolution

Coasts composed of resistant lithologies such as granite are generally highly resistant to erosion. They tend to evolve over multiple sea level cycles with highstands acting to remove subaerially weathered material. This often results in a landscape dominated by plunging cliffs with shore platforms rarely occurring. The long‐term evolution of these landforms means that throughout the Quaternary these coasts have been variably exposed to different sea level elevations which means erosion may have been concentrated at different elevations from today. Investigations of the submarine landscape of granitic coasts have however been hindered by an inability to accurately image the nearshore morphology. Only with the advent of multibeam sonar and aerial laser surveying can topographic data now be seamlessly collected from above and below sea level. This study tests the utility of these techniques and finds that very accurate measurements can be made of the nearshore thereby allowing researchers to study the submarine profile with the same accuracy as the subaerial profile. From a combination of terrestrial and marine LiDAR data with multibeam sonar data, it is found that the morphology of granite domes is virtually unaffected by erosion at sea level. It appears that evolution of these landscapes on the coast is a very slow process with modern sea level acting only to remove subaerially weathered debris. The size and orientation of the joints determines the erosional potential of the granite. Where joints are densely spaced (<2 m apart) or the bedrock is highly weathered can semi‐horizontal surfaces form. Copyright © 2014 John Wiley & Sons, Ltd.     

劈裂砂岩有、无砂粒填充条件下的多因素对渗流量影响对比分析

采用宜昌劈裂砂岩,在有、无砂岩填充条件下,分别从轴压、围压、劈裂面面积、凹凸高差、迹线长度、劈裂面2D投影面积、进出口长度、结构面粗糙度对渗流量的影响规律进行了对比分析。研究结果表明：有、无砂粒填充下轴压与渗流量均呈线性递增关系;无填充时围压与渗流量呈对数递减关系,有充填时围压与渗流量呈线性关系;无充填时渗流量与流面积呈三次函数关系,而充填后过流面积对渗流量几乎无影响;凹凸高差、2D面积与渗流量的关系也有相似规律,分析认为,这主要是砂粒充填后带来的过流通道要远大于上述三因素对过流通道的改变;无充填时,渗流量随迹线长度线性递减,有填充时该规律被淹没;无论有、无填充,渗流量与过流面粗糙度系数在一定范围内均呈现二次函数关系。这些规律能指导渗流测量时各因素的优先次序,可有效减少对次要影响因素的测量工作,同时可对渗流的数值模拟提供参考。     

断裂输导油气的机制及侧向分流控制因素探讨

断裂是具有复杂内部结构的地质体,是地下油气运移的重要通道。断裂可向空间各个方向输导油气,其中,纵向输导加侧向分流是断裂输导油气成藏的基本方式。在断裂活动周期的不同阶段,断裂输导油气的机制存在差异,特点也不尽相同;用圈闭充满度作为评定侧向分流强度的依据,分别比较储层、上覆泥岩、断层各要素与其相关性,综合评定认为上覆泥岩厚度是控制侧向分流的主要因素,储层厚度次之;总结认为,断裂输导具有“断-盖”联控的特点;珠一坳陷断裂输导成藏具有“双峰型”特征,区域性盖层与输导机制耦合控制了充注高峰分布。     

塔克拉玛干沙漠周边地区极端弱降水的时空变化特征

选用塔克拉玛干沙漠周边40个气象站1961-2009年日降水资料和4个极端弱降水指标,分析该地区极端弱降水的时空变化特征。采用M-K法和F检验对各站点降水指标的变化趋势及变化率进行检验和计算,并利用Monte Carlo模拟进行区域显著性检验。由 Copula函数得到两降水指标的联合分布,计算两降水指标的联合重现期。结果表明：（1）年最长连续无降水日数（CDD）多为80～100 d,呈显著减少趋势;出现频率最高的每年日降水量小于降水日序列25%分位数的日数（D₂₅）为0～10 d,呈显著增加趋势;每年日降水量小于降水日序列25%分位数的总降水量（P₂₅）的值集中在0～1.5 mm,2～3 mm的 P₂₅从2000年才开始出现;出现频率最高的每年日降水量小于降水日序列25%分位数的日平均降水量（I₂₅）为0.1～0.3 mm,I₂₅超过0.4 mm的情况极少出现。（2）CDD与D₂₅和P₂₅各自五年一遇值的空间分布相反。除CDD和D₂₅均大于各自五年一遇值的联合重现期较长外,其余各类型联合重现期较短。沙漠周边地区发生不同类型极端弱降水事件的概率不同。     

方钢管混凝土框架内隔板节点抗震性能的试验研究

本文设计了一榀三层两跨的方钢管混凝土框架模型,梁柱节点采用内隔板节点型式。采用拟静力试验方法,对方钢管混凝土框架施加低周反复水平荷载,研究了方钢管混凝土框架内隔板节点的荷载一位移曲线、节点延性、节点破坏机制和破坏特点等抗震性能。研究结果表明,方钢管混凝土框架内隔板节点的抗震性能较好。     

Geochemical types of pacific polymetallic nodules: An application of multivariate analysis

A total of 843 samples of Pacific Ocean polymetallic nodules (PNs) from five survey areas have been studied (metals analyzed: Mn, Fe, Ni, Cu, Co, Zn, Pb). The statistical analysis included the following techniques: factor R analysis, quick cluster Q analysis into 50 preclasses, various hierarchical cluster Q analyses (HCAs) using the preclasses (application of different HCAs to an identical set of data and of an identical HCA to two different subsets of the data), comparison of the HCA. The PNs of the survey areas can be grouped into five geochemical types (I‐V). The genesis of the PNs was interpreted as early diagenetic, hydrogenetic, and mixed (early diagenetic/hydrogenetic and hydrogenetic/hydrothermal. In addition, some further conclusions regarding the applicability of various HCA techniques depending on the structure of the data set have been drawn.     

The application of multivariate statistical methods to phytoplankton counts from the Hauraki Gulf,New Zealand

The phytoplankton population from a station in the Jellicoe Channel area of the Hauraki Gulf, New Zealand, was fairly constant, in terms of total population and species composition, throughout the year. Correspondence analysis enabled us to identify 3 groups of species. The largest of these comprised the core species which were present most of the time and included some, such as the coccolithophores, with a strongly seasonal occurrence. The species in the second group were mainly large centric diatoms and appeared for short periods during the winter months, apparently brought in by incursions of oceanic water. The third group of species occurred between April 1970 and October 1971 when there was a period of unusually warm weather: the winds were lighter and more often blowing onshore and this perhaps led to warmer, less nutrient‐rich surface waters being brought into the Gulf.     

突发地质灾害气象预警统计模型与应用

通过引入地质灾害潜势度,突发地质灾害气象预警统计模型解决了雨量判据法不能明确表达地质环境条件的问题,在此基础上,提出了潜势度计算、大气降雨变量设计、预警方程优化3方面的改进方法。为提高潜势度计算的准确性,增加了基于卡方检验的地质环境因子独立性判别步骤;对地质环境因子确信程度初始值和权值计算中确信程度变化量初始值设置进行了规定;并将预警模型中累计雨量修正为更为合理的有效累计雨量。在现有的预警方程的基础上提出了基于联合概率分析的预警方程,避免了其与基本地质认识和物理规律存在一定距离、方程系数的意义不明确的局限。以2009年7月2日发布的24 h雨量预报为例,计算结果表明：虽然预报区域面积从101 008 km²减小到27 553 km²,但是地质灾害点落入预报区的比例从44%增加到62%。这说明通过改进的预警模型理论上更加严密,空间准确率有所提高,空报率有所下降。